FIRST QUESTION: Can the United States actually do much at this very late time about the very large Soviet-Cuban involvement in the Horn of Africa? No. Direct American intervention is a fantasy. It doesn't look as though Washington, even through its worried friends in the region, can muster enough force to prevent Ethiopia from defeating Somali troops in the Ogaden region and secessionists in Eritrea province. The Soviet foray is no help to the general East-West atmosphere, but, still, the United States has good reason not to hold other interests like SALT hostage to the Horn.

Second question: How, then, should the United States treat the Soviet-Cuban intervention? However forlornly, it has got to recognize that the principle of territorial integrity in whose name the Kremlin is intervening is accepted by all but about two (Egypt, Sudan) of the 50-odd members of the Organization of African Unity. They are not equally happy to see communist power deployed on an African battlefield. But as long as Moscow confines its participation to clearing Ethiopian territory of invaders and rebels, they'll go along. To keep pointing up the geopolitical dimensions of the Soviet interventions, or to start loosely linking it to other East-West issues, as some White House officials in particular now are doing, is to miss the key African point. It is also to advertise American incapacity.

Third question: Does that mean the United States must simply sit quietly and be gored? No. American officials should call international attention to the Russians' repeated pledge, and to the Ethiopian government's own recent pledge to a Carter emissary, to fight only to the point where Ethiopia's integrity is restored. Their promise not to take revenge there-after on Somalia is one in which the United States, and the whole of the OAU, for their separate reasons, share a strong interest in seeing upheld. This means the Russians may indeed reap what gains in prestige and presence come from backing a winner. But it's not the end of the world. If Moscow takes this prize, nothing in its overall African performance suggests it will keep it for long. Occasions should be sought to continue the modest steps taken so far to show that the United States would appreciate a nonaligned Ethiopia.

Last question: Will that be the end of the Russians in Africa? Hardly. With a new intervention capability to test and flaunt, and with no important domestic drag on policy fancies, the Russians are clearly determined to have their run. The next likely place is Rhodesia, where they would enter in support of the only goal, "liberation," more meaningful to most Africans than territorial integrity. The answer, if there is one, is diplomatic preemption - to help establish a government that, by commanding the loyalty of most of its citizens, will provide a shrinking target for the sort of aggrieved gunmen the Russians customarily hitch their wagon to. In Somalia, diplomatic preemption did not so much fail; in the Soviets' and Americans' successive haste to establish a position in that unhappy place, it was fairly tried. The results for the United States, in the Horn, look to be disagreeable but not disastrous. In Rhodesia, it could be not much worse.